Rotary wing aircraft, such as helicopters, are very maneuverable at low speeds but have limited high speed capability. Compound aircraft with fixed and rotary wings are similarly limited unless the rotary portion can be stopped and stowed in a low drag configuration, which requires complex and heavy structure.
Rotor wing aircraft have been developed in which the wing acts as a rotor for vertical flight and becomes a fixed wing for high speed flight. A typical example is described in U.S. Pat. No. 3,159,360, entitled Jet Powered VTOL Aircraft. In this aircraft the same power source is used for forward propulsion and rotor wing drive, and a single control system operates the aircraft in both modes and through transition between the modes. To provide working clearance during the rotor phase of wing operation, the wing must be mounted on a pylon, or similar support, clear of the basic airframe. This has aerodynamic and structural disadvantages and requires some compromises in design and performance.
In the above referenced U.S. patent, the rotor wing is driven by tip jet propulsion, with propulsion gas ducted through the wing. This requires a thick airfoil section and is not practical in small aircraft. The problem is solved in one manner in U.S. Pat. No. 3,792,827, entitled VTOL Aircraft with Cruciform Rotor Wing. In this aircraft a separate tip jet powered member is mounted directly below and attached to the rotor wing. While suitable for some applications, this has aerodynamic disadvantages and still requires the wing to be mounted clear of the airframe.